The present invention relates generally to the field of measuring parameters of material. More particularly, the invention relates to a method and an apparatus for measuring parameters of a material by driving a sensing element with multiple simultaneous frequency signals, generating signals responsive to the frequency response of the material at each frequency, and processing the generated signals to determine the parameters of the material.
Various mobile and stationary machine systems use conveyors for moving bulk materials from place to place. Different types of conveyors are known, such as belt conveyors including endless canvas, rubber or metal belts which support the material being moved and are pulled over pulleys or rollers, chain or cable conveyors which include chains or cables adapted to pull plates, buckets or containers loaded or filled with material being moved, and auger or screw conveyors which include a helix formed about a turning shaft for moving material through a tube.
Mobile machine systems which use conveyors include various types of agricultural vehicles and construction equipment. Combines, for example, typically include a clean grain elevator for moving material up to a delivery auger, a delivery auger for moving the clean grain into the grain bin, a tailings auger for moving tailings to the tailings elevator to be returned to the threshing system of the combine, and an unloading auger for moving material from the grain bin to a transport device. Other examples include cotton pickers having a conveyor for moving cotton into storage bins, planters having a conveyor for moving seeds or fertilizer, and forage harvesters having a conveyor to move foraged material. Some conveyors include pneumatic delivery systems which are used, for example, to deliver seed from a seed bin to a planter or to convey forage from a forage harvester to a wagon. Stationary systems using conveyors include, for example, grain elevators using a conveyor including a driven chain which pulls paddles loaded with grain.
The machine systems described above may include real-time sensors and systems for measuring or monitoring parameters of material moved by the conveyors. These sensed parameters may include, for example, the yield or mass flow rate of material being moved by the conveyor, or the moisture content of the material. For example, yield and moisture sensors may be mounted to a grain auger of a combine to measure the mass flow rate and moisture content of grain flowing through the auger.
Known systems for measuring moisture may include capacitive sensors mounted in or on a fin which extends into the flow of material to measure the capacitance of the material. These systems extend into the flow of material so that the sensors can detect moisture despite their limited range. However, the intrusion into the flow of materials may cause certain materials, such as plant residue or sap, to build up on the sensors as contact is made with material being moved. The resulting build-up can cause the sensors to give inaccurate or erroneous readings. In addition, the intrusion of the sensors into the material may restrict or interrupt the flow of material, and the exposed fins and sensors are subject to mechanical wear and breakage.
Other measuring systems use capacitive sensors in a test cell which receives a small portion of the material flow diverted from the main flow. Such systems, however, require additional components and structures to divert the flow of material from the main flow and for the test cell, thereby increasing cost and decreasing reliability. Such systems may also suffer from build-up on the sensors since the material makes contact with the sensors.
Known sensors used to measure certain parameters of material being moved, such as yield or mass flow rate, may contain radioactive isotopes. These sensors may be subject to regulation concerning their sale and use since they are radioactive sources, thereby subjecting the user to the increased costs and paperwork associated with regulation compliance. The user is also exposed to the costs and risks generally associated with the use and management of radioactive sources. Other yield sensors generate signals when harvested grain hits a plate, the signals depending on both the amount of grain hitting the plate and the force at which the grain hits. These sensors may be inappropriate for measuring parameters of certain non-granular materials, such as forage, and may be difficult to integrate into a particular system.
Another problem with known systems for measuring parameters of a material includes the limited frequency response of such systems. Certain parameters of a material, such as type, mass flow rate, moisture content, density or other parameters, can be identified or measured by driving a sensing element with different frequencies and measuring the response of the material to each frequency. For example, one measuring system which uses a capacitive sensor in a test cell includes three fixed frequency generators which generate three fixed frequency signals and a multiplexer which sequentially applies the frequency signals to the sensor. The response at each frequency is then measured. This system, however, may be unable to provide required resolution over a given frequency range because of the fixed frequency signals. Moreover, expansion of this system to include a sufficient number of frequency generators to provide the required resolution over a given frequency range may be impractical because of the high number of frequency generators needed. Another measuring system includes a sweeping frequency oscillator which drives a capaciflector sensor. This latter system is able to generate more frequencies than the former system. However, when a dynamic system is being measured, the use of swept frequencies may introduce errors because the dynamic system may change over the time required to sweep the frequency signals.
Accordingly, the present invention provides an improved method and apparatus for measuring parameters of material. The parameters which can be measured include material type, moisture content, mass flow rate, density and other parameters. Parameters are measured by determining the frequency response of the material to multiple simultaneous frequencies. The frequency response can be determined over a wide frequency range with required resolutions without the need for a large number of frequency generators. The parameters are accurately measured even in dynamic systems wherein the values change over time. Material can be measured in test cells, or while being moved by conveyors such as augers, elevators or pneumatic conveyors. Different types of sensing elements can be used such as capacitive, capaciflector, resistive or inductive sensing elements.
One embodiment of the invention relates to a method for measuring at least one parameter of material including the steps of generating a plurality of frequency control signals corresponding to a plurality of frequencies, generating a plurality of frequency signals having frequencies selectable by the respective frequency control signals, combining the frequency signals to generate a combined frequency signal having a plurality of frequency components, applying the combined frequency signal as an excitation signal to a sensing element coupled to the material being measured, determining the frequency response of the material at each of the frequencies based upon output signals from the sensing element, and analyzing the frequency response of the material to determine the at least one parameter.
Another embodiment of the invention relates to an apparatus for measuring at least one parameter of material including a frequency generating circuit configured to generate a combined frequency signal having a plurality of frequency components selected in response to a plurality of frequency control signals, a sensing circuit coupled to the frequency generating circuit and including a sensing element coupled to the material being measured, wherein the combined frequency signal is applied as an excitation signal to the sensing element and the sensing element generates output signals based upon the frequency response of the material at each of the frequencies, a signal conditioning circuit coupled to the sensing circuit and configured to determine the frequency response of the material at each of the frequencies based upon the output signals from the sensing element, and a signal processing circuit to analyze the frequency response of the material to determine the at least one parameter of the material.
Another embodiment of the invention relates to a work vehicle including a support structure for supporting components of the work vehicle, a plurality of wheels coupled to the support structure to move the work vehicle on a surface, at least one of the wheels being powered to move the work vehicle along the surface, and at least one conveyor to move material from a first location to a second location on the work vehicle. The work vehicle further includes a frequency generating circuit configured to generate a combined frequency signal having a plurality of frequency components selected in response to a plurality of frequency control signals, a sensing circuit coupled to the frequency generating circuit and including a sensing element coupled to the at least one conveyor, wherein the combined frequency signal is applied as an excitation signal to the sensing element and the sensing element generates output signals based upon the frequency response of the material being moved at each of the frequencies, a signal conditioning circuit coupled to the sensing circuit and configured to determine the frequency response of the material at each of the frequencies based upon the output signals from the sensing element, and a signal processing circuit configured to analyze the frequency response of the material to determine the at least one parameter of the material.
Another embodiment of the invention includes an apparatus for measuring at least one parameter of material. The apparatus includes a noise generating circuit configured to generate a noise signal having a substantially even power spectrum across at least a range of frequencies, a sensing circuit coupled to the noise generating circuit and including a sensing element coupled to the material being measured, wherein the noise signal is applied as an excitation signal to the sensing element and the sensing element generates output signals based upon the frequency response of the material, a signal conditioning circuit coupled to the sensing circuit and configured to determine the frequency response of the material at multiple frequencies based upon the output signals from the sensing element, and a signal processing circuit configured to analyze the frequency response of the material to determine the at least one parameter of the material.